1. Field of the Invention
The present invention relates to a heat treatment apparatus for heating a semiconductor wafer, a glass substrate, or other substrates by light irradiation.
2. Description of the Background Art
Conventionally, lamp annealers employing halogen lamps have been commonly used in the step of activating ions in a semiconductor wafer after ion implantation. Such lamp annealers carry out the activation of ions in a semiconductor wafer by heating (or annealing) the semiconductor wafer to a temperature of the order of, for example, 1000° C. to 1100° C. Such heat treatment apparatuses utilize the energy of light emitted from halogen lamps to raise the temperature of a substrate at a rate of about several hundred degrees per second.
In recent years, with increasing degree of integration of semiconductor devices, it has been desired that the junction be made shallower with decreasing gate length. It has turned out, however, that, even if the activation of ions in a semiconductor wafer is carried out with such a lamp annealer as described above that raises the temperature of a semiconductor wafer at a rate of about several hundred degrees per second, there occurs a phenomenon that boron, phosphorus, or other ions implanted in the semiconductor wafer are deeply diffused by heat. The occurrence of such a phenomenon gives rise to apprehension that the junction may become deeper than the desired level, hindering good device formation.
There has thus been proposed a technique for raising temperature only in the surface of an ion-implanted semiconductor wafer in an extremely short time (several milliseconds or shorter) by irradiating the surface of the semiconductor wafer with flash light, using xenon flash lamps (hereinafter simply referred to as “flash lamps”). The xenon flash lamps have a spectral distribution of radiation ranging from ultraviolet to near-infrared regions. The wavelength of the light emitted from the xenon flash lamps is shorter than that of the light emitted from conventional halogen lamps, and it almost coincides with a fundamental absorption band of a silicon semiconductor wafer. Thus, when a semiconductor wafer is irradiated with the flash light emitted from the xenon flash lamps, it is possible to rapidly raise the temperature of the semiconductor wafer, with only a small amount of light transmitted through the semiconductor wafer. It has also turned out that the flash light emitted within an extremely short time of several milliseconds or shorter allows a selective temperature rise only near the surface of a semiconductor wafer. That is, the extremely short temperature rise by the xenon flash lamps allows the ion activation without deep diffusion of ions.
As an example of the heat treatment apparatus employing the xenon flash lamps, U.S. Pat. No. 4,649,261 and WO 03/085343 disclose heat treatment apparatuses that carry out desired heat treatment by the combined use of pulsed-light-emitting lamps, such as flash lamps, located on the front side of a semiconductor wafer, and continuously-illuminated lamps, such as halogen lamps, located on the underside. The heat treatment apparatuses disclosed in U.S. Pat. No. 4,649,261 and WO 03/085343 raise the temperature of a semiconductor wafer, first to a certain level by using the halogen or other lamps and then to a desired processing temperature by pulse heating from the flash lamps.
In the mechanism for heating by light irradiation from both sides of a semiconductor wafer, temperature uniformity is greatly affected by the shape of the inner wall of a chamber for receiving the semiconductor wafer. Specifically, since neither the light emitted from halogen lamps nor the light emitted from flash lamps are collimated light, the light is partly reflected off the inner wall of the chamber to enter the semiconductor wafer. Thus, if the inner wall surface of the chamber is non-uniform along the circumference of the semiconductor wafer, the reflected light entering the semiconductor wafer becomes non-uniform, which results in a non-uniform in-plane temperature distribution in the wafer.
It is, however, an absolute necessity for the chamber to have a transport opening for transporting a semiconductor wafer therein and thereoutside, so that the inner wall surface of the chamber is essentially non-uniform at the location of the transport opening. The transport opening is formed not annularly along the circumference of the semiconductor wafer but only in part of the chamber. This causes another problem that the portion of a semiconductor wafer that is opposed to the transport opening with no side wall will have a lower temperature than the other portion because of a small amount of incident light thereon, which results in a non-uniform in-plane temperature distribution in the semiconductor wafer.